1. Field of the Invention
This invention relates to the preparation of organic sulfide compounds of improved color from olefinic materials.
2. Prior Art
Various proposals have been made for producing organic sulfides by treating olefins with sulfur chlorides and then reacting the resulting intermediate with compounds containing sulfur. For example, organic polysulfides may be prepared by the sulfochlorination of olefins containing 6 or more carbon atoms and further treatment with inorganic higher polysulfides according to Eby U.S. Pat. No. 2,708,199. In addition, Myers U.S. Pat. No. 3,471,404 discloses that sulfurization reactions of this nature may be carried out by reacting a sulfochlorinated isobutylene intermediate product with a mixture of an alkali metal sulfide and free sulfur in a molar ratio of at least 2:1 followed by a further prolonged treatment with aqueous sodium hydroxide, apparently for reducing high chlorine contents, in producing extreme pressure additives. Beretvas et al U.S. Pat. No. 3,068,218 indicates that sulfochlorinated products of improved color may be obtained by sulfochlorinating polymers of propylene, etc. containing 8 or more carbon atoms in an aqueous reaction mixture and then sulfurizing the intermediate with a solution of sodium sulfide in water and isopropanol in producing products with sulfur contents of the order of 10 to 34 % by weight. In Kimball U.S. Pat. No. 2,249,312, the sulfochlorinated adduct of amylene or higher olefins is treated with sodium sulfide and/or other alkaline compounds to produce stable products of relatively low sulfur content and generally high chlorine contents.
In general, prior art organic sulfide compounds have one or more such undesirable characteristics as high cost, low sulfur content and corrosive attack on metals and alloys used in machinery. Products having a chlorine content above 2% and also those produced from sodium polysulfide reactants are usually rather corrosive. These disadvantages can be overcome and organic sulfide compounds having improved properties, especially as to high sulfur content and low corrosion characteristics, obtained by the economical process described in application Ser. No. 2,349 filed on Jan. 12, 1970 by A. G. Horodysky in which the aqueous alkali metal monosulfide reactant employed in the final reaction is derived from a spent effluent stream resulting from hydrocarbon purification operations and consequently of low commercial value. However, it has been found that a very dark or black product is occasionally obtained in that process with some olefinic hydrocarbon reactants, and the same undesirable product coloration is believed to occur quite frequently in the aforesaid prior art methods. While there is no evidence that the black color in any way reduces the effectiveness of the material as an additive for extreme pressure lubricants, such discoloration does seriously affect its marketability. Customers have a strong aversion to accepting a black product, particularly when the normal color of such material is yellow or orange or light red. The instant invention is based upon the discovery of a technique for inhibiting such discoloration of the product.